Thrombin is an important activator of both fibrin clot formation and platelet plug formation and plays a central role in hemostasis, thrombosis, and atherosclerosis. Thrombin is an active form of an enzyme normally present in plasma as an inactive precursor, prothrombin. When vascular damage exposes tissue factor to the circulation, prothrombin is converted to thrombin, thus making the enzyme available to activate platelets.
Thrombosis in arterial circulations is a leading cause of death today. Platelet activation by thrombin is believed to be a critical event in the development of arterial thrombosis. Based on structure-activity studies of a cloned platelet thrombin receptor, two antagonists of thrombin and thrombin receptor function were designed. Hung et al., J. Clin. Invest. 89:444, 1992. The first antagonist, an xe2x80x9cuncleavablexe2x80x9d peptide mimicking the receptor domain postulated to interact with thrombin, was shown to be potent thrombin inhibitor. The second, a proteolytically inactive mutant thrombin designed to bind but not cleave the thrombin receptor, was also found to be a specific antagonist of receptor activation by thrombin.
Stimulation of platelets has also been shown to result in the release of various mediators that may lead to an extension of inflammation and intensify the immune response. Recent reports have suggested that platelets may play an important role in the inflammatory process of human asthma. Therefore several researchers have been studying the effects of thrombin on platelet aggregation and its effects on asthma.
Nedocromil sodium is used therapeutically as an antiinflammatory drug in the treatment of asthma. Roth et al., J. Allergy Clin Immunol., 91(6):1217, 1993, demonstrated that nedocromil sodium interferes with thrombin- and platelet activating factor-mediated platelet activation. The inhibition of platelet activation demonstrated in these studies was proposed to contribute to the antiinflammatory effects of nedocromil sodium in asthma.
Thrombin stimulation of human platelets has also been shown to result in the release of a preformed proteinaceous human eosinophil (Eo) chemotactic activity. Kameoyoshi et al., J. Exp Med. 176:587, 1992. This finding was suggested to serve as additional evidence for the recent understanding that platelets contribute to inflammatory reactions of allergic asthma.
It has now been found that thrombin potently and effectively increases cytosolic calcium release in human airway smooth muscle, which is required for smooth muscle contraction and stimulates human airway smooth muscle cell proliferation. Inhibition of the activities of thrombin upon human airway smooth muscle through use of thrombin receptor antagonists and/or antithrombin agents is useful as a treatment of bronchospasm and asthma.
An object of the present invention is to provide a method of inhibiting cytosolic calcium release in human airway smooth muscle cells that comprises treating human airway smooth muscle cells with an effective amount of an antithrombin agent so that release of cytosolic calcium is inhibited. The use of antithrombin agents to inhibit cytosolic calcium release in these cells is also provided.
Another object of the present invention is to provide a method of inhibiting proliferation of human airway smooth muscle cells comprising treating human airway smooth muscle cells with an effective amount of an antithrombin agent so that proliferation of human airway smooth muscle cells is inhibited. The use of antithrombin agents to inhibit proliferation of these cells is also provided.
Yet another object of the present invention is to provide a method of treating asthma in an individual suffering from asthma comprising administering to said individual an effective amount of an antithrombin agent so that smooth muscle contraction and proliferation of smooth airway smooth muscle cells which occurs in individuals suffering from asthma is inhibited. The use of antithrombin agents to treat asthma is also provided.